There is a growing consensus among climate scientists that the increasing concentration of heat trapping carbon dioxide (CO2) in the atmosphere—mainly from combustion of fossil fuels—is contributing to global warming. Consequences of global warming include melting of polar ice caps and rising sea levels, threatening arctic ecosystems and endangering coastal communities.
Climate scientists argue that during most of human history—up to the industrial revolution—the air held no more than 275 ppm CO2. The atmospheric CO2 concentration in 2009 was 385 ppm and rising. To slow down global warming, CO2 from high fossil fuel emission sources such as coal-fired power plants, needs to be captured and “returned” to the ground—essentially reversing the fossil fuel mining, processing, and combustion process.
A number of CO2 capture and storage (CCS) technologies have been developed. The storage of CO2 has also been referred to as CO2 sequestration. One method for CCS uses metal oxide solutions, such as potassium or magnesium oxide, to remove CO2 from flue gas or other CO2 containing vent gases. The general capture mechanism involves reaction of the metal oxides with CO2 to form metal carbonates. These carbonate salts can either be land-filled, or be regenerated via oxidation to form a concentrated CO2 stream that can be compressed and injected into geological formations for storage.
Conventional gas absorption units, commonly referred to as scrubbers, may be used to remove CO2 from flue gas using the metal oxide solutions as absorption liquids. Other CO2 absorption liquids include amine systems. With amine systems, the absorption liquid is typically regenerated and a concentrated CO2 stream is formed for compression and in ground storage.
Although these gas absorption methods are technically mature, their use in CCS applications has been limited. This is in part due to the fact that not all geological formations are well-suited for CO2 storage. Perhaps more importantly, the hesitation to adopt such CCS processes stems from the fact that the investment and operating cost for capture, compression and storage of CO2 brings the carbon emitting plant owner no corresponding financial return.
Biomass burial and ocean storage have also been proposed for carbon sequestration. In the biomass burial and ocean storage approach, the carbon capture occurs naturally through photosynthesis, wherein sunlight and CO2 combine to form carbonaceous biomass. However, the efficiency and effectiveness of this approach has been questioned. Unless stored under a controlled environment underground, the biomass is likely to decompose and re-release the CO2. In certain environments, the biomass may undergo anaerobic decomposition into methane which has been reported to have a heat trapping efficiency 23 times higher than CO2. Furthermore, as in the case of other prior art CCS processes, there is little economic incentive for adoption of this method.
More recently, algae growth and harvesting technologies have been adapted to carbon capture systems and apparatuses. Since algae growth is typically limited by rate of CO2 supply, algae ponds and bioreactors have been designed to remove CO2 from stationary emission sources. US patent publications 2007/0048848 and 2009/0162922 describe such systems, apparatus, and methods. In some embodiments, CO2 rich flue gas from a coal-fired power plant is directed to an algae photo-bioreactor, where it undergoes photosynthetic conversion algal biomass. However, like terrestrial plants, algae are biodegradable. Upon decomposition, the fossil fuel-based CO2 is released into the atmosphere. Consequently, a profitable and effective method of CO2 capture and storage is needed.
One aspect of the present invention is production of bio-based polyolefins, basic chemicals, and hydrogen. Bio-based ethylene may be obtained from dehydration of ethanol. More recently, U.S. Pat. No. 7,288,685 has reported that olefins may be obtained by fluidized catalytic cracking of vegetable oils—although at lower yields than from steam cracking of hydrocarbons. However these processes require construction of new and expensive plants. Furthermore, these olefin production routes are not believed to be competitive with steam cracking of hydrocarbons, which is the technology used in all world scale olefin plants today. Consequently, a method of producing bio-based olefins utilizing existing steam crackers is desired.
Another aspect of the present invention is the production of bio-based motor gasoline components, suitable for use as spark-ignition engine fuels. Although the biofuel prior art provides various methods and systems for producing such compositions, the prior art methods and systems do not address early adoption issues such as capital costs for building new plants. By providing a method wherein existing petrochemical plants can be used to produce such fuels, the present invention addresses this important need.